1. Field of the Invention
The present invention relates to a process for the preparation of heterosubstituted acetals by reaction of heterosubstituted vinyl compounds with alkyl nitrites in the presence of palladium in metallic or bonded form.
Heterosubstituted acetals of the formula (I) specified later on below are suitable as starting materials for the synthesis of other organic compounds, such as medicaments, plant protection agents or dyes. Thus, for example, diethyl 2,2-dimethoxyethylphosphonate can be employed for the chain lengthening of ketones and aldehydes (Org. Synth. 53 (1973), 44-48). The transacetalization of this compound leads, furthermore, to phosphorus-containing polymers (J. Polym. Sci. 22 (1984), 3335-3342; J. Polym. Sci. A 26 (1988), 2997-3014); polymers of this type are employed in the sectors of flameproofing agents, hydrometallurgy and membrane technology.
Phenylsulphonyl-acetaldehyde diethyl acetal is reacted in accordance with DE-A 34 19 750 to give precursors for the preparation of pyrethroids.
Phenoxysulphonyl-acetaldehyde dialkyl acetal can be converted to 1,2-benzoxathiine 2,2-dioxide, which can be reacted in accordance with EP 128 116 and EP 337 947 to give herbicides.
2. Description of the Related Art
The literature describes with sporadic cases the preparation of acetals by reaction of the parent olefins with alkyl nitrites in the presence of palladium salts. Thus, for example, EP 55 108 describes the oxidation of compounds such as ethene, propene, butylene, cyclohexene, acrylic esters and acrylonitrile. The yields obtained in these oxidations, however, are low, so that any industrial utilisation would have to take account of considerable expenditure on production isolation and on the recycling of catalyst and solvent. In particular, the gas phase reaction proposed in EP 55 108 cannot be used for preparing acetals of the formula (I) specified later on below, since at the high temperature necessary for this reaction the occurrence of decomposition reactions and other secondary reactions would have to be expected.
J. Heterocyclic Chem. 29(1992), 1625 describes the reaction of 2-nitro-styrenes with alkyl nitrites in liquid phase, with the simultaneous addition of oxygen, to give the corresponding acetals. However, this reaction may give rise to ignitable mixtures, a fact which--especially in the case of industrial implementation--leads to a relatively high expenditure for the provision of the necessary safety measures.
The literature consequently contains only processes which can be used to react unsubstituted olefins, or olefins which are mono- or disubstituted on at least one carbon atom with a further carbon atom; in particular, the literature contains no processes which can be used to convert heterosubstituted vinyl compounds to acetals. Owing, however, to the many possible applications of heterosubstituted acetals, there was a need to provide processes for their preparation.